Option Explicit
'mois est la plage A2:A31 que j'ai nommée. Onglet Formules > Définir un nom
Private Sub Worksheet_Change(ByVal Target As Range)
Dim d As Long, dt1 As Range, dt2 As Range
Application.EnableEvents = False
Set dt1 = Range("e1")
Set dt2 = Range("a1")
dt2 = dt1
If Not Intersect(Target, [mois]) Is Nothing Then
If IsDate(Target) Then
d = Day(Target) + 1
Else
d = Target
End If
If IsDate(DateSerial(Year(dt1), Month(dt1), d)) Then
Target = Year(dt1) & "-" & Month(dt1) & "-" & d
End If
End If
If IsEmpty(dt1) Then Range("mois").ClearContents
Application.EnableEvents = True
End Sub